Spinning apparatus with converging gas streams

ABSTRACT

Apparatus and method for producing filamentary material by extruding substantially axially through an orifice comprising contacting the extruded filament stream downstream of the orifice and prior to hardening with a plurality of converging, substantially planar, high velocity gas streams, each moving substantially in the direction of the filament stream such that they converge upon the filament stream at an angle of from about 45* to 5* from the axis of the polymer extrusion nozzle. The planes of the gas streams intersect at a point which is at a distance measured perpendicularly from the axis of the extrudate stream at least equal to the diameter of the extrudate stream.

United States Patent [191 McGinnis et a1.

[ SPINNING APPARATUS WHTH CONVERGING GAS STREAMS [75] Inventors: Paul H.McGinnis, Kings Mountain; William 1). McLaughlin, .lr.; Robert E.Swander, both of Charlotte, all of [73] Assignee: Celanese Corporation,New York,

[22] Filed: July 30, 1973 [21] Appl. No.: 383,631

Related U.S. Application Data [62] Division of Ser. No. 237,832, March24, 1972, Pat.

UNITED STATES PATENTS Hartmann 265/210 F X 1 WWW. 19, 197% 12/1970Wagner 425/72 4/1972 Stalego et al. 65/16 57 xnsrnxcr Apparatus andmethod for producing filamentary material by extruding substantiallyaxially through an orifice comprising contacting the extruded filamentstream downstream of the orifice and prior to hardening with a pluralityof converging, substantially planar, high velocity gas streams, eachmoving substantially in the direction of the filament stream such thatthey converge upon the filament stream at an angle of from about 45 to 5from the axis of the polymer extrusion nozzle. The planes of the gasstreams intersect at a point which is at a distance measuredperpendicularly from the axis of the extrudate stream at least equal tothe diameter of the extrudate stream.

1 Claim, 8 Drawing Figures PATENTEL :13! 1 91914 3, 49,04

sum 2 or 4 PATEME rm 1 91974 SHEET Q 0F 4 Fig, 6

SPINNING APPARATUS WITll-ii CONVERGING GAS STREAMS This is a division,of application Ser. No. 237,832, filed Mar. 24, i972, now Pat. No.3,787,265 issued Jan. 22, 1974.

BACKGROUND OF THE INVENTION This invention relates to the production offilamentary material. It is particularly concerned with novel apparatusfor spray spinning molten fiber-forming polymers to form nonwovenstructures.

Various proposals have been advanced heretofore in connection withintegrated systems for forming fibrous assemblies, such as nonwovenfabrics and the like, directly from molten fiber-forming materials. Ingeneral, the proposed systems envisioned an extrusion operation followedby collection of the extruded filamentary material in the form of acontinuous fabric, web or other desired fibrous assembly. When detailsare considered, however, the various proposals differed in substantialways.

In recently issued US. Pat. No. 3,543,332, a novel method for sprayspinning molten fiber-forming polymers is shown. Filamentary material isextruded substantially axially through an orifice and contacteddownstream prior to hardening by a plurality of high velocity gasstreams, each moving in a direction having a major component in thedirection of extrusion of the filament stream in a shallow angle oftangential conver gence therewith to attenuate the filament stream. Theaxis of the gas passages and corresponding gaseous streams are skewedabout the extrusion orifice such that they have non-intersecting axesspaced about the axis of the extrusion orifice.

The present invention is concerned with an improved apparatus for thedirect production of filamentary materials. It is an object of thepresent invention to provide improved apparatus for spray spinningmolten fiber-forming materials at production rates much higher than theprior art processes. At the same time, it is a further object of theinvention to produce a substantially uniform spray-spun fibrousstructure while minimizing the formation of shot or objectionally shortfibers which detract from the desirability of the collected fibrousassembly.

In accordance with an embodiment of the invention, spinning nozzle meansare provided with an extrusion orifice with a fiber-forming material andwith a plurality of substantially rectangular gas outlet passages spacedapart from the extrusion orifice to supply jets of high velocity gas forattenuating the extruded filament stream prior to hardening of thefilaments. The molten polymer and attenuating gas do not flow throughthe same nozzle or any other part of the spray-spinning equipment; Thegas passages are separated from the extrusion orifice by an insulatingmeans such as an air space. As a consequence, the gas flow, if it is notheated, would not cause heat transfer from the polymer to the gas. Suchan arrangement eliminates the need for either heating the attenuatinggas or heating the polyattenuating or drawing the material leaving theextrusion orifice. Further, the gas passages are positioned such thatthe planar gas streams are directed substantially inthe direction offlow of the extrudate stream in such a manner that the gas streamsconverge upon the extrudate stream. The planes of the gas streams andthe planar projections of the gas outlet passages intersect at a pointwhich is at a distance measured perpendicularly from the axis of theextrudate stream at least equal to the diameter of the extrudate stream.The planes of the attenuating gas streams contact the polymer extrudatestream at an angle of from about 45 to 5 from the axis of the polymerextrusion nozzle to project it away from the extrusion orifice.

Briefly, a relatively heavy monofil is extruded and a plurality ofstreams of gas, e.g., steam or air, are directed at a shallow angle inthe direction of flow of the freshly extruded monofil. This attenuatesthe monofil into relatively fine denier material and, like the moreconventional drawing, also increases the tenacity of the solidifiedextrudate. Depending upon the conditions of extrusion, the filamentarymaterial will be one or more substantially continuous structures, orrelatively long staple fibers, or conventional length fibers, possiblymixed with varying amounts of solid debris orshot.

The severity of the gas streams varies the attenuation and determinesthe denier of the resulting fibrous material which may range from about0.1 up to about 50, although for maximum surface and strength the fiberdenier is preferably mostly below about 25 denier. Actually each productwill include a range of deniers which will add to its strength andperformance. I The extrudate is discharged onto a suitable collectionsurface such as a rotating collector drum. The height or length of theresulting structure can be set by traverse or by use of multiple'side-by-side extruders whose spray patterns overlap. The duration ofspray obviously controls the thickness of the resulting structures. Theconditions of extrusion and collection are such that each new layer whendeposited is sufficiently tacky so as to adhere to the preceding layerso that the total structure will be shape-retaining without furthertreatment.

The filament-forming material may comprise any known suitable polymericmaterial which is plasticizable, soluble or fusible. If solublematerials are used in conjunction with a solvent, the problem of solventremoval is encountered which, of course, is avoided where fusiblematerials are employed. Representative fusible materials includepolyolefins such as homopolymers and copolymers of olefins, e.g.ethylene and prop ylene, especially stereospecific or crystallinepolyethylene and polypropylene; polyamides such as nylon 66, nylon 6,and the like; polyesters such as polyethyleneterephthalate; celluloseesters such as cellulose acetate, and especially the secondarytriacetate; polyurethanes; polystyrene; polymers of vinylidene monomerssuch as vinyl chloride, vinyl. acetate, vinylidene chloride, andespecially acrylonitrile; and mixtures thereof.

DESCRIPTION OF THE DRAWINGS A more complete understanding of these andother features of the invention will be gained from a consideration ofthe following detailed description of an embodiment illustrated in theaccompanying drawings in which:

FIG. 1 is a schematic illustration of an extrusion and collectionapparatus in accordance with the present invention;

FIG. 2 is a schematic plan view of the extrusion apparatus and processin accordance with the present invention;

FIG. 3 is a graph illustrating vectorially the forces resulting from twoconverging planar gas streams;

FIG. 4 is a schematic illustration showing how the vector forceequipment illustrated in FIG. 3 both deflect and accelerate the filamentstream.

FIG. 5 is a front elevation of one embodiment of an extrusion nozzle andplanar attenuating gas jets useful in the apparatus and processillustrated in FIG. 2;

FIG. 6 is a schematic perspective illustration of an extrusion nozzlehaving a pair of planar attenuating gas jets positioned on each side ofthe extrusion nozzle;

FIG. 7 is a perspective view of a planar attenuating gas jet shown inFIG. 6.

FIG. 8 is a schematic front elevation of the preferred arrangement forutilizing four extrusion nozzles.

Referring now more particularly to the drawings, in FIG. 1 afiber-forming, thermoplastic polymer, preferably a polyolefin, is fed toan extruder 10 provided with an adapter section 12 to which a gas, suchas steam or air, is supplied-While extrusion temperatures may beanywhere above the melting point of the polymer, it has been found thatbest results are obtained by heating the polymer to at least 150C., andpreferably from about 250 to about.350C. above the softening point ofthe polymer being extruded. For example, polypropylene havinghereinafter defined characteristics will generally be heated totemperatures of from about 325 to about 400C. Polyethylene, on the otherhand, will be heated to from about 350 to about 450C. A hot, moltenstream of polymer 16 is discharged through a nozzle 14.

It is to be understood that nozzles having one or more polymer orificesmay be used. Also, a plurality of nozzles per collector may be employed.However, there must be at least two planar gas streams per polymerorifice. The attenuating gas orifices 18 are of an elongated rectangularcross section, as shown in FIGS. 5 and 6, to emit substantially planargas streams 17.

The gas streams 17 act on the polymer stream 16 in convergence region 20to form an attenuated filament 22 wherein it cools and partiallysolidifies while moving toward collection surface 24 on which it iscollected as a cylindrical structure 26. The collection surface 24 isordinarily rotated at a speed sufficient to provide a moving surface offrom about 25 to about 125 feet per minute by a motor drive. Collectionsurface 24 is in surface contact with roller 28, which acts as an idlerroll and whose bias against the mandrel can be adjusted; the extent ofthe bias will effect how tightly the tacky filament packs againstprevious layers on the cartridge 26. Both the collection surface 24 andthe roller 28 are reciprocated laterally by a traversing mechanism 30whose throw determines the shape of the cylinder; the throw may be ofconstant length or may change in the course of package build-up toproduce a particular shape as may be needed for acceptance in areceptacle of predetermined corresponding shape.

The force of the attenuating gas on the polymer stream causes thepolymer to attenuate greatly, e.g.,

from '10 to 500 times, based on diameter ratios, and possibly fibrillateto a slight degree to produce a substantially continuous fiber. Someturbulence and resultant whipping about of the polymer stream occurs.Consequently, a generally random, stereo reticulate structure of fiberresults as the material impinges on the collector. Since the polymer isstill in a somewhat molten or tacky state when it strikes the collector,some sticking together occurs at the points where fiber intersects. Forbrevity, this sticking will be referred to as interfiber bonding,although it is to be understood that this bonding will ordinarily resultfrom an individual fiber looping about and sticking or bonding toitself.

For best results, the collection surface 24 should be from about 6 toabout 48 inches, preferably 10 to 30 inches, from polymer exit nozzle14. With greater dis tances the spray pattern is difficult to controland the resultant web tends to be nonuniform. Shorter distances resultin a web which contains too great a quantity of shot, i.e., beads ofnon-attenuated polymer, which undesirably affects subsequent processing,web uniformity and surface area.

In FIG. 2 there is schematically shown a top view of the apparatus ofthis invention. A plurality of converging substantially planar gasstreams 17 (corresponding substantially to planar projections of gasoutlet passages 18) issue from substantially rectangular gas outletpassages 18. The axis 19 of the nozzle 14 corresponds to the directionin which the polymer stream is extrucled. The gas jets 17 are positionedalong side the extrusion nozzle 14 in such a manner that the gas streams17 are directed substantially in the direction of flow of the polymerextrudate along the nozzle axis 19. The planes of the gas streams andplanar projections of the gas outlet passages intersect at a point 21which is at a distance B measured perpendicularly from intersectionpoint 21 to the nozzle axis 19. The distance B is at least equal to thediameter of the'extrudate stream at a point 23 along the nozzle axis injuxtaposition to the point of intersection 21. Preferably B is at least0.06 inch, most preferably from about 0.2 to 2.0 inches. The point 23,which defines the perpendicular distance from the nozzle 14 to theintersection point 21 is a distance A of at least 2.0 inches from thepoint of'extrusion nozzle 14, preferably from about 2.5 to 7.0 inches.The attenuating gas jets 18 are positioned along side the extrusionnozzle such that the planes of the attenuating gas streams 17 intersectthe nozzle axis 19 (also the axis of the extrudate stream) at an angle(a, and 01 less than 45 to more than about 5, preferably from about 10to 40, to project the extrudate stream away from the extrusion nozzle.

In FIG. 3 the force of the gas streams 17 are shown vectorially. The Yforce component is'in the direction of the extrusion nozzle axis andpolymer extrudate stream, and serves to accelerate and attenuate theextrudate stream.

Angles a, and a shown in FIG. 2, are not the same so that theintersection point of the planes of the gas streams is off the nozzleaxis and extrudate stream. FIG. 4 shows that the effect of this is todeflect the extrudate stream 16, first to one side and then to theother, in addition to attenuating the extrudate. If a, and ar areidentical, the planar filament streams 18 would intersect on the nozzleaxis and substantially on the extrudate stream. As can be seen from theexamples, this leads to much lower surface area when compared to themethod of this invention illustrated in FIG. 2. It is probable that theeffect of the gas streams intersecting onthe extrudate streamis to cutthe stream and produce a less open, lower surface area product.

The illustrated extrusion nozzle 14 has a center polymer exit orifice15, as shown in FIG. 5, which ordinarily sect the axis of the extrudatestream at angles a, and 04 of about 30 and 25 respectively. Thepolypropylene extrudate is collected on a metal drum having adiameter'of 1 inch to produce annular cylindrical structures.

has a diameter of from about'0.0l to about 0.10 inch, 5 The totalthroughput of polypropylene is about 6 lb./hr. and preferably from about0.015 to about 0.030 inch. The procgdure is repeated, except that theeXtru-der throughput is increased such that the total throughput In thepreferred embodiment, polymer 1s generally f polypropylene b i SpraySpun. i 9 lbjh extruded through the nozzle at 1 to about 30 lb./hr., anddesirably at 5 to 15 10/10. 10 AM Along side polymer exit orifice l5, asshown in FIGS. Polypropylene, as in Example 1, is spray spun Sand 6, area plurality of attenuating substantially rectthrough one or morecircular orifices, utilizing planar angular elongated gas orlfices l8havlng a width of attenuating gas jets, as shown in FIG. 6, spacedatadisfrom about 0.002 to about 0.050 inch, preferably from tance of 2inches from the axis of each extrusion oriabout 0.004 to about 0.025inch, and a length of at fice. The spray spun structure was collected ona cylinleast about0.5 inch, preferably from aboutl.0 to about dricaldrum. The process conditions for 14 runs are 3.0 inches. Attenuating gasnozzles 18 emit substansummarized in Table 1 below:

TA LE 1 Distance Extru Polymer Collector from Surface Extru sionThrough- Speed Nozzle to area sion orifice No. of Air Air put (FeetCollection (square Run Temp. diameter ori- Flow Pressure (lbs/ A B a, 01per drum meters No. (C) (in) ficcs (CFM) (PSlG) hr) (in) (in) min.) (in)per gram] 2 395 0.010 4 50 05 0 4 5/10 30 30.0 040 2a 395 0.010 4 50 050 4 5/10 25 23.5 0.45 2b 395 0.010 4 50 05 9 4 5/10 30 25 30.0 0.33 Zr395 0.010 4 50 05 9 4 5/10 30 25 8.5 0.35 2.1 3110 0.010 4 59 05 0 4 027 27 32.0 0.31 20 330 0.010 4 59 05 9 4 0 27 27 32.0 0.27 2] 1 3950.010 4 57 00 0 3 5/10 38 29 73 30.5 0.53 lg 395 0.010 4 57 00 9 3 5/1038 29 73 30.5 0.42 2h 395 0.010 4 57 00 0 3 0 34 34 73 39.5 0.30 21 3950.010 4 57 00 9 3 0 34 34 73 3 9.5 0.31 Zj 330 0.0114 1 30 2.5 3 0 34 3420 41.0 0.48 :1- 350 0.010 1 30 35 2.5 3 5/10 33 29 20 41.0 0.58 21 3500.018 1 30 35 2.5 4 0 27 27 20 41.0 0.38 2m 350 0.0111 1 30 35 2.5 45/10 30 25 20 41.0 0.43

tially planar gas streams 17 and are positioned, as illus The moleculesin the surface layer of a solid are trated in FIGS. 2 and 8. bound onone side to inner molecules but there is an FIGS. 6 and 7 show, inperspective, a preferred emimbalance of atomic and molecular forces onthe other. bodiment of a gas jet for emitting a substantially planar Thesurface molecules attract gas, vapor, or liquid molgas stream. The gasenters through gas inlet passage 25 ecules in order to satisfy theselatter forces. The attracand is emitted through rectangular elongatedgas orition may be either physical or chemical, depending on fice 18. tthe system involved and the temperature employed.

' EXAMPLE 1 Physical adsorption (frequently referred to as van der Waalsadsorption) is the result of a relatively weak in- Isotacticpolypropylene having an intrinsic viscosity teraction between a solidand a gas. This type of adof 1.5 and a melt flow rating of 30is'spray-spun at a sorption has one primary characteristic. Essentiallyall melt temperature of 390C. through four extrusion oriof a gasadsorbed can be removed by evacuation at the fices arranged as shown inFIG. 8. Each orifice is of a same temperature at which it was adsorbed.substantially circular crosssection having a diameter of While the firstgas molecules to contact a clean solid about 0.016 inch. Referring toFIG. 8, two planar attenare held more or less rigidly by van der Waalsforces, uating gas jets, as shown in FIG. 6, were spaced at a distheforces active in the condensation of vapors become tance of 2 inchesfrom the axis of each extrusion nozincreasingly responsible for thebinding energy in subzle, in approximately parallel relationship to eachother sequent layer development. The expression along side eachextrusion orifice. The elongated rectangular air jets had an orificewidth of 0.010 inch and a VmCP/(P P) [I (C 1) Wm] length of about 1.88inches and each emitted ambient (1) air flowing at a rate of about 56cubic feet per minute 60 at a pressure of about p.s.i,g where V is thevolume of gas adsorbed at pressure P,

Ref ri g to FIG, 2, th gas jets 17 are positioned so V the volumeadsorbed when the entire surface is covthat the planes of gas streams l8intersect at a point 21 ered by a monomolecular layer, C a constant, andP, which is at a distance B of five-.sixteenths inch from the thesaturation pressure of the gas (actually the vapor axis of the extrudatestream which corresponds to noz- 65 pressure at a given temperature of alarge quantity of zle axis 19. The distance A which defines the distancefrom the orifice 14 to the intersection point 21, is 4 inches. As aresult, the planes of the gas streams intergas condensed into a liquid),is obtained by equating the rate of condensation of gas molecules ontoan adsorbed layer to the rate of evaporation from that layer and summingYfor an infinite number of layers. The expression describes the greatmajority of low temperature adsorption data. Physical measurements ofthe volume of gas adsorbed as a function of pressure at a fixedtemperature, therefore, permit calculation of V,,., the volume of gasrequired to form a layer 1 molecule thick. Equation 1 can be rearrangedto the linear form Then a plot of data for P/V,,(P, P) versus P/P givesa straight line, the intercept and slope of which are l/V C and (C l)VC, respectively. The value of V is thus readily extracted from a seriesof measurements. From this information and knowledge of the physicaldimensions of single molecules, the surface area of the adsorbing solidis computed.

Asshown in Table'l above, surface area measurements were taken utilizingOrr Surface Area Pore Volume Analyzer (Model 2100A). The runs using thepreferred process of this invention (2, 2a, 2b, 2c, 2f, 2g, 2k and 2m)exhibited a higher surface area than the runs wherein the attenuatinggas streams intersected on the axisof the extrudate stream. A directcomparison can be between runs 2f and 2h, 2g and 21', 2j and 2k,

and 21 and 2m. Increases in surface area of from 0.05 to 0.17 meterslgram are achieved.

The higher the surface area, the greater the filtration efficiency ofthe structure.

The preferred fiber-forming polymers employed in the present inventionare the polyolefins, such as polyethylene or polypropylene. The meltindex of the polyolefin prior to extrusion will ordinarily be from about5 to 60 and preferably from about to 40. The intrinsic viscosity will befrom about 1.0 to about 2.5 and preferably from about 1.0 to about 2.0.

Instead of the polyolefins, one may also employ other thermoplastic,melt-extrudable, fiber-forming polymers such as polyamides, polyesters,phenol-formaldehyde resins, polyacetals, and cellulose esters, e.g.,cellulose acetate. With some of the polymers, spray spinning is aided bymixing the polymer with a melt depressant to facilitate melting withoutdecomposition.

Air will normally be employed as the attenuating gas for reasons ofeconomy. Other gases, e.g., steam, nitrogen, helium, etc., are alsosuitable. Usually,, the attenuating gas will be at ambient temperature.Heated gas, e.g., at a temperature of 250 to 500C, may also beadvantageously used, however.

It will be appreciated that the instant specification and examples areset forth by way of illustration and not limitation, and that variousmodifications and changes may be made without departing from the spiritand scope of the present invention.

We claim:

1. Apparatus for producing organic thermoplastic filamentary materialcomprising nozzle means having an extrusion orifice for fiber-formingmaterial and a plurality of substantially rectangular gas outletpassages shaped so as to emit substantially planar gas streams, said gasoutlet passages being spaced from said extrusion orifice and separatedfrom said nozzle means by an insulating means, said gas outlet passagesbeing so positioned with respect to the nozzle means such that: l) thegas passages are closer to the axis ofthe extrusion orifice at theoutlet end of the passage than at an interior zone of the passage so asto direct the gas stream in a convergence angle with the axis of theextrusion orifice of from about 5 to 45, 2) no two of the planar'projections of the gas outlet passages converge and intersect with theaxis of the extrusion orifice at the same angle, and 3) planarprojections of the gas outlet passages intersect at a point which is ata distance measured perpendicularly from the axis of the extrusionorifice at least equal to the diameter of 'the extrudate stream at apoint along the extrudate stream in juxtaposition to the point ofintersection of the planar projections of the gas outlet passages, andmeans for supply- .ing said gas passages with gas under pressure to beprojeeted from said passages to contact andv attenuate the stream offiber-forming material issuing from said extrusion orifice.

1. Apparatus for producing organic thermoplastic filamentary materialcomprising nozzle means having an extrusion orifice for fiber-formingmaterial and a plurality of substantially rectangular gas outletpassages shaped so as to emit substantially planar gas streams, said gasoutlet passages being spaced from said extrusion orifice and separatedfrom said nozzle means by an insulating means, said gas outlet passagesbeing so positioned with respect to the nozzle means such that: 1) thegas passages are closer to the axis of the extrusion orifice at theoutlet end of the passage than at an interior zone of the passage so asto direct the gas stream in a convergence angle with the axis of theextrusion orifice of from about 5* to 45*, 2) no two of the planarprojections of the gas outlet passages converge and intersect with theaxis of the extrusion orifice at the same angle, and 3) planarprojections of the gas outlet passages intersect at a point which is ata distance measured perpendicularly from the axis of the extrusionorifice at least equal to the diameter of the extrudate stream at apoint along the extrudate stream in juxtaposition to the point ofintersection of the planar projections of the gas outlet passages, andmeans for supplying said gas passages with gas under pressure to beprojected from said passages to contact and attenuate the stream offiber-forming material issuing from said extrusion orifice.